Photoluminescent markings with functional overlayers

ABSTRACT

A photoluminescent marking that includes a photoluminescent layer and at least one functional overlayer is disclosed. The photoluminescent layer comprises at least one type of photoluminescent material. The at least one functional overlayer is adapted to selectively filter wavelengths of radiation to enhance the daylight observability of a final emission signature of the marking or to prevent the observability with the naked eye of a printed message on the marking. Also methods of making and using the inventive photoluminescent marking are disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/102,100 filed on May 6, 2011 now U.S. Pat. No. 8,097,843, titled,“Photoluminescent Markings with Functional Overlayers,” which in turn isa continuation of Ser. No. 12/487,362, now U.S. Pat. No. 7,960,688 filedJun. 18, 2009 of the same title, each of which are incorporated byreference herein in their entirety for all purposes.

FIELD OF THE INVENTION

The present invention relates generally to photoluminescent markingsthat can be used for stealth detection and further wherein thefunctionality of such photoluminescent markings is enhanced with the useof one or more functional overlayers, that is, one or more layersapplied over the photoluminescent layer. The functional overlayers canrender the daylight color of the photoluminescent markings to a widerange of colors, or increase the stability of the photoluminescentmarkings against photolytic degradation of the infrared emissions fromsuch markings, or enhance the daylight detectability of such markings,or enable a printed message to be camouflaged, or combinations thereof.The present invention also relates to objects containing the markingsand methods of using them.

BACKGROUND OF THE INVENTION

Photoluminescent materials and compositions that containphotoluminescent phosphorescent materials which have emissions in thevisible region of the electromagnetic spectrum have been disclosed. Forexample, metal sulfide pigments which contain various elementalactivators, co-activators and compensators have been prepared whichabsorb at 200-400 nm and have an emission spectrum of 450-520 nm.Further examples of sulfide photoluminescent phosphorescent materialsthat have been developed include CaS:Bi, which emits violet blue light;CaStS:Bi, which emits blue light; ZnS:Cu, which emits green light; andZnCdS:Cu, which emits yellow or orange light.

The term “persistence” of phosphorescence is generally a measure of thetime, after discontinuing irradiation, it takes for phosphorescence of asample to decrease to the threshold of eye sensitivity. The term“long-persistent phosphor” historically has been used to refer toZnS:Cu, CaS:Eu,Tm and similar materials which have a persistence time ofonly 20 to 40 minutes.

Recently, phosphorescent materials that have significantly higherpersistence, up to 12-16 hours, have been reported. Such phosphorsgenerally comprise a host matrix that can be alkaline earth aluminates(oxides), alkaline earth silicates, or alkaline earth aluminosilicates.

Although methods for uniquely marking and identifying objects havereceived thought and attention, such methods do not enable stealthdetection. Thus, stealth detection refers to a method of identificationwherein the emissions from the photoluminescent markings are notordinarily observable by a human observer but detectable by friendlyagents or friendly forces with specific detection equipment, and furtherwherein activation is not required during detection. This condition ofnot requiring activation during detection is important for the conceptof stealth detection as the energy required for activation, such as byusing a laser, is potentially detectable and hence revealing of thepresence of the detector. Markings that enable stealth detection will beof high value in the combat theater for combat equipment or personnel.High persistence markings with emissions in the infrared region forstealth detection or stealth identification have been disclosed in U.S.Pat. Appl. No. 2008/185,557 and U.S. Pat. Appl. No. 2008/121,818 both toAgrawal et al.

Whether the photoluminescent markings enable stealth detection or notthe specific marking itself may not be a stealth marking. Stealthmarkings are those wherein the markings themselves are created such thatit is not readily apparent that the object has been marked foridentification. This can only be achieved when the daylight color of thephotoluminescent markings enable either the markings to blend in withthe area surrounding the marking so as not to be distinguishable fromthe surrounding area, or wherein their daylight color is such that it isrevealing of a marking that is normally present, such as a white oryellow color road marking. Photoluminescent markings that have emissionin the infrared, such as those in referenced in U.S. Pat. Appl. No.2008/185,557 and U.S. Pat. Appl. No. 2008/121,818, will generally bedark in color. Hence they can function as stealth markings only in verylimited situations. The prior art is silent on how to make thesemarkings function as stealth markings in a wide variety of environments.

In the field of markings for identification there is a need for markingsthat not only enable stealth detection or stealth identification butwherein the markings themselves are created such that it is not readilyapparent that the object has been marked for identification, that is,the marking is a stealth marking. Such markings will be of great valuein a variety of anti-terrorist activities, in the combat theater andalso in anti-counterfeiting applications. The use of a functionaloverlayer, that is, a layer applied over the photoluminescent layerwhich contains carefully selected colorants can be of great value inadjusting the daylight color of photoluminescent markings that haveemissions either partially or wholly in the infrared, whether or not themarkings have been enabled for stealth detection, thereby camouflagingthe presence of the marking.

Infrared emitting markings cited in U.S. Pat. Appl. No. 2008/185,557 andU.S. Pat. Appl. No. 2008/121,818 both to Agrawal et al have alsodisclosed the use an overlayer on top of the photoluminescent layer forthe purpose of protecting the photoluminescent layer from physicaldamage and/or ensuring that any residual visible emission will not bedetected. However there is no disclosure in these applications for theuse of an overlayer to adjust the daylight color of the photoluminescentmarking so as to render it as a stealth marking. These applications alsodo not disclose the use of an overlayer to enhance the daylightdetectability of the photoluminescent markings. Nor do theseapplications disclose the use of an overlayer for the enhancement ofphotolytic stability of the underlying photoluminescent layer.

Photoluminescent materials, even if they are inorganic materials, can besubject to photolytic degradation. Even though ZnS phosphorescentmaterials have been known for a long time, their use for outdoorapplications has been precluded because of photolytic instability.Additionally fluorescent materials, including fluorescent materialscontemplated in this invention, can be sensitive to degradation byphotolytic activity. Although use of UV absorbers, singlet oxygenscavengers, anti-oxidants, HALS (hindered amine light stabilizers) havebeen widely reported in the literature, such materials, by themselves,are not sufficient to impart the required photolytic stability of themarkings of this invention to promote outdoor use of such markings.

It can therefore be seen from the above discussions that there is a needfor photoluminescent markings whose emission is partly or fully in theinfrared region of the electromagnetic spectrum, such emissions beingsuitable for stealth detection or not, wherein the markings haveadjustable daylight color, or have improved photolytic stability, orhave enhanced daylight detectability, or combinations thereof. There isalso a need for methods of creating and using the inventivephotoluminescent markings as well as objects containing thephotoluminescent markings.

SUMMARY OF THE INVENTION

The present invention provides for photoluminescent markings thatcontain a photoluminescent layer which has an emission signature thatlies partly or fully in the infrared region of the electromagneticspectrum and one or more functional overlayers applied over thephotoluminescent layer. Such functional overlayers can be used, forexample, to significantly increase the range of daylight colorsattainable by such photoluminescent markings so as to enhance their useas stealth markings, or to significantly increase the photolyticstability of such markings, or to enhance the detectability of thephotoluminescent layer in daylight, or to camouflage a printed message,or combinations thereof, while at the same time minimally impacting theinfrared emissions from such markings. Other functional layers may beenvisioned to include, for example, layers which reduce or eliminate anyresidual visible radiation, layers which increase the efficiency ofconverting the exciting or activating radiation to infrared, and/orlayers to aid in the activation of the photoluminescent underlayer. Theuse of multiple functional overlayers will result in achieving multiplefunctionalities as described above. The photoluminescent layer overwhich the functional layers are applied may contain one or morephotoluminescent phosphorescent materials, one or more photoluminescentfluorescent materials or a combination thereof.

It should be pointed out that when the functional overlayer is used forconcealment, that is, for stealth marking, it contains materials whichconceal the presence of the photoluminescent layer by independentlyadjusting the daylight color of the marking, that is, the visible colorof the marking can be adjusted to be different from that of thephotoluminescent layer. The use of the functional overlayer allows for amuch greater degree of freedom in adjusting the daylight observablecolor. With the proper selection of the colorant materials, one canensure that any reductions in intensity of the emissions from thephotoluminescent layer are minimized, that is, that the functionaloverlayer has an adequate level of transparency both to the excitingradiation and to the infrared emissions.

Further, the present invention relates to methods of stealth detectionby creating and using the inventive photoluminescent markings as well asto objects containing the inventive markings.

Thus, in a first aspect, the present invention provides forphotoluminescent markings which contain a photoluminescent layer whichcontain selected photoluminescent materials and one or more functionaloverlayers wherein the markings emit fully or partially in the infraredregion of the electromagnetic spectrum.

In a second aspect, the present invention provides for photoluminescentmarkings which contain a photoluminescent layer which contain selectedphotoluminescent materials and one or more functional overlayers thatcontain selected colorants that adjust the daylight color of themarkings to either blend imperceptibly with the surrounding area of anobject to which the markings are applied or to indicate a marking thatwould normally be present, wherein the markings emit fully or partiallyin the infrared region of the electromagnetic spectrum.

In a third aspect, the present invention provides for photoluminescentmarkings which contain a photoluminescent layer which contain selectedphotoluminescent materials and one or more functional overlayers thatcontain selected materials which have absorptions in selected regions ofthe electromagnetic spectrum so as to increase the photolytic stabilityof the markings, wherein the markings emit fully or partially in theinfrared region of the electromagnetic spectrum.

In a fourth aspect, the present invention provides for photoluminescentmarkings which contain a photoluminescent layer which contain selectedphotoluminescent materials and one or more functional overlayers thatcontain selected materials that enhance the daylight observability ofthe infrared emission, wherein the markings emit fully or partially inthe infrared region of the electromagnetic spectrum.

In a fifth aspect, the present invention provides for photoluminescentmarkings which contain a photoluminescent layer which contain selectedphotoluminescent materials and a functional overlayer that containsselected materials that increase the photolytic stability of themarkings, and a second functional overlayer that contains selectedcolorants that adjust the daylight color of the markings to either blendimperceptibly with the surrounding area of an object to which themarkings are applied or to indicate a marking that would normally bepresent, wherein the markings emits fully or partially in the infraredregion of the electromagnetic spectrum.

In a sixth aspect, the present invention provides for photoluminescentmarkings which contain a photoluminescent layer which contain selectedphotoluminescent materials and a functional overlayer that containsselected materials that enhance the daylight observability of theinfrared emission, and a second functional overlayer that containsselected colorants that adjust the daylight color of the markings toeither blend imperceptibly with the surrounding area of an object towhich the markings are applied or to indicate a marking that wouldnormally be present, wherein the markings emits fully or partially inthe infrared region of the electromagnetic spectrum.

In a seventh aspect, the present invention provides for photoluminescentmarkings which contain a photoluminescent layer which contain selectedphotoluminescent materials and a functional overlayer that containsselected materials that enhance the daylight observability of theinfrared emission, and a second functional overlayer that containsselected materials that increase the photolytic stability of themarkings and a third functional overlayer that contains selectedcolorants that adjust the daylight color of the markings to either blendimperceptibly with the surrounding area of an object to which themarkings are applied or to indicate a marking that would normally bepresent, wherein the markings emits fully or partially in the infraredregion of the electromagnetic spectrum.

In an eighth aspect, the present invention provides for,photoluminescent markings which contain a photoluminescent layer whichcontain selected photoluminescent materials and a functional overlayerthat contains selected colorants used for the purpose of camouflaging aprinted message which can be text, graphs, numerical or combinationsthereof, and which has been printed on either the photoluminescentlayer, or one of the functional overlayers of the aforementioned aspectsor on combinations thereof.

In a ninth aspect, the present invention provides for photoluminescentmarkings which contain a photoluminescent layer which contain selectedphotoluminescent materials and a functional overlayer that containsselected colorants that adjust the daylight color of the markings toeither blend imperceptibly with the surrounding area of an object towhich the markings are applied or to indicate a marking that wouldnormally be present, and/or selected stabilizing materials that increasethe photolytic stability of the markings, and/or selected materials thatenhance the daylight observability of the infrared emission, and/orselected materials which camouflage a printed message which has beenprinted on either the photoluminescent layer, or one of the functionaloverlayers of the aforementioned aspects or on combinations thereof,wherein the markings emits fully or partially in the infrared region ofthe electromagnetic spectrum.

In a tenth aspect, the present invention provides for photoluminescentmarkings of the foregoing markings aspects wherein any or all of thefunctional overlayer is generally between 25 and 350 microns when dry.

In an eleventh aspect, the present invention provides for a reflectivelayer under the photoluminescent layers of the photoluminescent markingsof any of the aforementioned aspects of the inventive markings.

In a twelfth aspect, the present invention provides for photoluminescentmarkings which contain a photoluminescent layer which contain selectedphotoluminescent materials and a functional overlayer that containsselected colorants used for the purpose of camouflaging a printedmessage which can be text, graphs, numerical or combinations thereof;and which has been printed on the reflective layer below thephotoluminescent layer.

It should be noted that the functional overlayer that is used forrendering the marking as a stealth marking, that is, the functionaloverlayer in which the daylight color is adjusted so as to either blendimperceptibly with the surrounding area of an object to which themarking is applied, or, when applied to objects that typically havenonphotoluminescent markings for traditional usage, renders a daylightcolor indicative of such traditional markings, the layer has to be thetop most observable layer so as to form the visible top surface of thestealth marking.

In an thirteenth aspect, the present invention provides forphotoluminescent marking of the foregoing marking aspects wherein thephotoluminescent layer over which the functional overlayers are appliedcontain one or more photoluminescent phosphorescent materials, one ormore photoluminescent fluorescent materials or a combination thereof.

In a fourteenth aspect, the present invention provides for methods ofdetecting or identifying a photoluminescent marking containing the stepsof applying a photoluminescent marking of any of the aforementionedmarking aspects onto at least a portion of an object, then activating orcharging the marking and detecting the infrared emission.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a shift in emission spectra resulting fromincorporation of photoluminescent phosphorescent and photoluminescentfluorescent dyes. Chart a) is the representative absorbance spectra, b)is the representative emission spectra and c) is the representative netemission spectrum resulting from the inventive composition. Asillustrated, a photoluminescent phosphorescent material absorbsradiation at A1 from an excitation source. The photoluminescent phosphorcan continuously emit radiation E1 which overlaps with the absorptionspectra A2 which emits radiation at E2. E2 again is designed to overlapwith the absorption A3 which emits radiation E3. This process cancontinue until a final desired emission is obtained, in this case E5. Ascan be seen from chart c) the composition is designed to emit radiationat approx. 780 nm.

FIG. 2 illustrates an object (10) upon which has been applied aphotoluminescent layer of the current invention (12), and a functionaloverlayer (14) of the current invention.

FIG. 3 illustrates an object (10) upon which has been applied areflective layer (16), a photoluminescent layer of the current invention(12), and further a functional overlayer (14) of the current invention.

FIG. 4 illustrates an object (10) upon which has been applied aphotoluminescent layer of the current invention (12), a functionaloverlayer of the current invention (14), and further a second functionallayer of the current invention (18) beneath the functional overlayer(14).

FIG. 5 illustrates an object (10) upon which has been applied areflective layer (16), a photoluminescent layer of the current invention(12), a functional overlayer of the current invention (14), and furthera second functional layer of the current invention (18) beneath thefunctional overlayer (14).

FIG. 6 illustrates an object (10) upon which has been applied aphotoluminescent layer of the current invention (12), a functionaloverlayer of the current invention (14), and further a second functionallayer of the current invention (18) and a third functional overlayer ofthe current invention (22), both beneath the functional overlayer (14).

FIG. 7 illustrates an object (10) upon which has been applied areflective layer (16), a photoluminescent layer of the current invention(12), a functional overlayer of the current invention (14), and furthera second functional layer of the current invention (18) and a thirdfunctional overlayer of the current invention (22), both beneath thefunctional overlayer (14).

In FIG. 8, FIG. 8 a illustrates a carrier layer (20) upon which has beenapplied a functional overlayer of the current invention (14), andfurther a photoluminescent layer of the current invention (12). FIG. 8 billustrates the application of the construct in FIG. 8 a to an object(10) such that the photoluminescent layer (12) is in intimate contactwith the object (10). FIG. 8 c illustrates the construct of FIG. 8 bafter the carrier layer (20) has been removed.

DETAILED DESCRIPTION OF THE INVENTION

In the current invention, detection whether it is stealth or otherwise,results from photoluminescent layers containing photoluminescentmaterials that have emissions in the infrared region of theelectromagnetic spectrum, and further wherein the value of such markingshave been enhanced by the use of one or more functional overlayers. Onesuch functional overlayer contains materials that adjust the daylightcolor of the photoluminescent stealth markings so as to either beindicative of a marking that might be normally present or to blend withthe surrounding area of the object to which the marking is appliedthereby enhancing the value of the marking by rendering it as a stealthmarking. Other functional overlayers of the current invention containselected materials that increase the photolytic stability of themarkings. Another functional overlayer of the current invention containsselected materials that enhance the daylight observability of themarking. Another functional overlayer contains materials that camouflagea printed message which can be printed on either the reflective surface,or the photoluminescent layer, of any of the underlying functionaloverlayers or combinations thereof. The overlayers of the presentinvention are designed to have minimal impact on both the excitationregion that activates the photoluminescent markings as well as theinfrared emissions from the markings.

Unless otherwise noted, percentages used herein are expressed as weightpercent.

As used herein, “photoluminescent” materials are luminescent materialsthat are capable of being excited by electromagnetic radiation and“photoluminescence” is the emission of electromagnetic radiation causedby the excitation.

As used herein, a “phosphorescent” material is a material that has theability to be excited by electromagnetic radiation into an excitedstate, but the stored energy is released gradually. Emissions fromphosphorescent materials have persistence, that is, emissions from suchmaterials can last for seconds, minutes or even hours after theexcitation source is removed. The released energy may be in the form ofUV, visible or infrared radiation.

As used herein, a “fluorescent” material is a material that has theability to be excited by electromagnetic radiation into an excited stateand which releases energy in the form of electromagnetic radiationrapidly, after excitation. Emissions from fluorescent materials have nopersistence, that is, emission essentially ceases after an excitationsource is removed. The released energy may be in the form of UV, visibleor infrared radiation.

As used herein, “luminescence”, “phosphorescence” or “fluorescence” isthe actual release of electromagnetic radiation from a luminescent,phosphorescent or fluorescent material, respectively.

As used herein “persistence” is defined as the time it takes, afterdiscontinuing irradiation, for photoluminescent emissions emanating froma photoluminescent object to decrease to the threshold detestabilitywith a suitable detection apparatus.

As used herein “high persistence” is defined to mean that the time ittakes, after discontinuing irradiation, for photoluminescent emissionsemanating from a photoluminescent object to decrease to the thresholddetestability with a suitable detection apparatus is greater than threehours.

As used herein, “electromagnetic radiation” refers to a form of energycontaining both electric and magnetic wave components which includesultraviolet (UV), visible and infrared (IR) radiation.

As used herein, an “emission signature” refers to the specific emissionspectrum of the photoluminescent composition as a result of activation,such emission being characterizable by wavelength, amplitude and/orother desired parameters.

As used herein, “Stokes shift” refers to the difference in wavelengthbetween the excitation or activation wavelength and the emissionwavelength of photoluminescent materials.

As used herein, a “liquid carrier” is a liquid that acts as a carrierfor materials distributed in a solid state and/or dissolved therein.

As used herein, a “layer” is a film resulting from a compositioncontaining at least one film-forming polymeric resin and a liquidcarrier that is substantially dry.

As used herein, a “photoluminescent layer” is defined as a layercomprised of an admixture of materials which is capable of emittingelectromagnetic radiation from electronically-excited states whenexcited or charged or activated by electromagnetic radiation. It shouldbe noted that the photoluminescent layer may contain one or morephotoluminescent phosphorescent materials, one or more photoluminescentfluorescent materials, or combinations thereof.

As used herein, the term dried refers to the condition whereinapproximately less than 12 weight % of a liquid carrier remains. Notethat in addition, that is, beyond the residual liquid carrier, it ispossible, if necessary, to also have plasticizer materials present inthe dried layer.

As used herein “stealth identification” and “stealth detection” refer tothe act of identifying or detecting a photoluminescent marking or anobject containing the photoluminescent marking, wherein the emissionsfrom the markings are ordinarily not visible to a human observer eitherduring daytime or nighttime and wherein the photoluminescent markingsare not required to be activated during detection (that is, activationand detection are decoupled spatially and temporally) and furtherwherein emissions from such markings require specific detectionequipment for observation.

As used herein “spatially and temporally decoupled” means that detectioncan be practiced after the activation has ceased (temporally) as well asdetection can occur away from the marking, or the object containing themarking and/or its activation source (spatially).

As used herein, a marking is defined as a “stealth marking” when it hasbeen selectively formulated so that its daylight color blends in withthe surrounding area upon which it has been placed or is indicative of amarking that is typically present for traditional usage.

As used herein the phrase “blending with the surrounding area” meansthat a photoluminescent marking intended to be a stealth marking isrendered such that its daytime color closely resembles the color of thesurrounding area, or, when applied to objects that typically havenon-photoluminescent markings for traditional usage, renders a daylightcolor indicative of such traditional markings,

As used herein, the term “transmits” refers to the process of allowingenergy to pass through a material, or layer.

As used herein, the term “colorants and colorant materials” includesmaterials that can adjust observable color by absorption only, and/or byfluorescence and/or by phosphorescence.

As used herein “CAS is a unique numerical identifier assigned to everychemical compound, polymer, biological sequences, mixtures and alloysregistered in the Chemical Abstracts Service (CAS), a division of theAmerican Chemical Society.

Photoluminescent markings of the current invention emit fully or partlyin the infrared region of the electromagnetic spectrum that may or maynot have been enabled for stealth detection. A key advantage of thephotoluminescent markings of the current invention is that they can beformulated to be activated or excited without necessarily requiringspecialized sources. In those cases wherein they are formulated so as tonot require specialized activating sources, they can be charged withnaturally-occurring illumination essentially for most of the day, be itduring the morning, noon or evening, as well as on cloudy days, inaddition to artificial sources such as metal halide lamps.Photoluminescent markings of this invention that have been enabled forstealth detection, whether activated by naturally or artificiallyoccurring illumination, will not require activating equipment at thepoint of identification or detection, and will enable detection to bepractices at daytime or nighttime and at locations away from thephotoluminescent markings and/or its detection source, as well as afterthe activation of the marking has ceased. Further, with the use of highluminous intensity and persistent photoluminescent phosphorescentcompositions such as those described below in the photoluminescentlayer, stealth markings can be created that allow stealth detection atdaytime or nighttime and can be practiced at great distances from thestealth markings and/or its activation source and long after activationhas ceased.

For the case wherein the photoluminescent layer of the photoluminescentmarkings of the current invention contain only photoluminescentfluorescent materials so as to yield emissions either fully or partiallyin the infrared, the markings can be excited by electromagneticradiation from the ultraviolet to the infrared region of theelectromagnetic spectrum. It should be noted that emissions from suchmarkings will not have persistence, that is, they are not enabled forstealth detection at nighttime. However, during daytime with naturalillumination as well as typical artificial illumination they will notrequire separate activation equipment.

For the case wherein the photoluminescent layer of the photoluminescentmarkings of the current invention contains phosphorescent materials forpersistence, such markings should be charged with electromagneticradiation within the excitation spectrum of the phosphorescent materialswhich is generally in the UV and/or short blue region. When suchphosphorescent materials have been admixed with fluorescent materials,the combination of which will emit fully or partially in the infraredregion of the electromagnetic spectrum, the markings will be enabled forstealth detection when excited with electromagnetic radiation that is inthe region of the excitation spectrum of the phosphorescent material. Itshould be noted however that because of the presence of fluorescentmaterials these markings will also be excited with radiation thatoverlaps with the excitation spectrum of any of the fluorescentmaterials.

The use of the combinations of photoluminescent materials andfluorescent materials, or for the case wherein only photoluminescentfluorescent materials are used in the photoluminescent layer, a certaindaylight color will be imparted to the marking resulting from such alayer. Colorants in the form of pigments or dyes, added to thephotoluminescent layers, wherein such colorants are absorptive ofvisible electromagnetic radiation, can be used to make some adjustmentsto the daylight color. However, not only will such color adjustment beextremely limited but they will interfere with the attainment of thedesired infrared emissions.

It has now been discovered that by applying a functional overlayer overthe photoluminescent layer one can attain a greater degree of freedom toadjust the daylight color, while at the same time minimizing any adverseimpact on the infrared emission from the photoluminescent layer. Byadding colorants, whether absorptive only, or fluorescent, orcombinations thereof, to the functional layer will not only hide thedarker color of the underlying photoluminescent layer, but will alsoenable the markings to be rendered in a variety of colors. It should beemphasized that the colorant materials for the functional overlayershould be selected such that they have adequate transparency to both theexciting and emitting radiation.

The functional overlayer is formulated to allow charging energy to passthrough the functional overlayer to charge or activate thephotoluminescent layer and at the same time allow the resultant infraredemissions to pass back out through the functional overlayer. Thefunctional overlayer is formulated to create daylight color of themarkings such that either the color of the marking blends with the colorof the surrounding area of the surface or object to which the markingsare applied, or to create a color that would be naturally present in theenvironment, such as, for example, a yellow or white stripe markingtypically present on a road surface.

The functional overlayer can also be used for creating markings for thecase of a surface or object that is multicolored, such as with acamouflage pattern. The colors of the markings can be adjusted to besimilar to the various camouflage colors and the marking can be appliedin more than one part so as to recreate the pattern and thus blend withthe surrounding area.

Markings deploying the functional overlayers as described above can beused as stealth markings, whether for stealth identification ordetection or not. Because the functional overlayer is formulated withselected colorants to blend in with the color of the surrounding area ofthe surface or object to which the markings are applied, it camouflagesthe presence of the underlying photoluminescent layer.

The markings of this invention which enable stealth detection and whichhave been rendered as stealth markings through the use of a functionaloverlayer are intended for use both in daylight and at nighttime.Normally, in the absence of a functional overlayer during daytime, thephotoluminescent layer not only converts the emissions of thephosphorescent material into infrared emissions but also converts anyincident visible radiation into infrared emission. The photoluminescentlayer materials will also cascade any shorter wavelength energy, shorterrelative to the final emission, into infrared emission. Thus, althoughthe signal-to-noise ratio is a lot poorer in daylight, for example,using night vision scopes equipped with appropriate daylight filters(high pass or band pass filters), the infrared emissions from thesemarkings can be readily detected even during daylight. However, the useof colorants in a functional overlayer, specifically colorants withbroad absorption in the visible region, can decrease the daylightdetectability of these markings. This however can be overcome to asignificant degree by the use of another functional overlayerspecifically aimed at converting lower levels of incident daylightradiation into infrared emission. It should be noted that such afunctional overlayer, when used in conjunction with another functionaloverlayer that adjusts the daylight color of the marking, will not onlyimprove the detectability of both the daylight and nighttime emissionsbut also enable the marking to function as a stealth marking.

Another functional overlayer of the present invention contains selectedmaterials that absorb visible radiation which causes photolyticinstability of the underlying photoluminescent materials. Thefluorescent materials, whether admixed with phosphorescent materials ornot, used in this invention to convert the excitation radiation toinfrared emission can be vulnerable to photolytic degradation byradiation within and/or near their absorption spectrum. Use of typicalstabilizing agents such as UV absorbers, antioxidants, singlet oxygenscavengers, etc is not sufficient to impart the required degree ofphotolytic stability. It has been discovered that by modulatingradiation near their excitation spectrum with a functional overlayer toselectively filter such radiation, one can significantly increase thestability of such fluorescent materials to photolytic degradation. Carehas to be exercised, similar to the case of the functional overlayer foradjusting the daylight color, to ensure that the absorptive materialsselected to selectively filter the radiation responsible for thedamaging photolytic activity of the photoluminescent material allowcharging energy to pass through the functional layer to charge oractivate the photoluminescent layer and at the same time allow theresultant infrared emissions to pass back out though the functionaloverlayer. Examples of absorptive materials that meet the aforementionedcriteria are described in the set of examples below.

Another functional overlayer of the current invention can be used tocamouflage a printed message. A text message, a graphic message or acombination thereof may be printed with an ink that is normally visibleto the naked eye. Such a message can be printed either over thereflective layer, over the photoluminescent layer or over one of thefunctional overlayers, such as, for example, the functional overlayerthat enhances the daylight observability of the photoluminescentmarkings. As long as there is a functional overlayer that containsselected colorants which absorb visible light over the printed message,such a message will be camouflaged but detectable both at daytime (withappropriate filtration or contrast enhancement) and night time withinfrared detecting equipment. As long as the ink used for printing willabsorb the infrared emissions from the marking, it will provide acontrast to be visible with infrared detection equipment such as nightvision devices. As before, care has to be exercised that the colorantshave adequate transparency to both the exciting and emissive radiation.

The above functional overlayers can be used alone to provide oneparticular desired function or they can be used in combination with eachother to provide a combination of more than one function.

The photoluminescent layer of the immediate invention is comprised ofphotoluminescent phosphorescent materials or photoluminescentfluorescent materials or combinations thereof. When present in thephotoluminescent layer, it is generally preferred that thephosphorescent materials be such that they have emissions that are ofhigh intensity and persistence. The phosphorescent materials aregenerally charged or activated by UV and/or short blue energy that areincident upon it. The emission from the photoluminescent phosphorescentmaterials exhibits a downward Stokes shift to energy lower than theenergy used to excite the photoluminescent phosphor. When thephotoluminescent layer contains both phosphorescent materials andfluorescent materials, emissive energy from the phosphorescent materialscan be absorbed by a fluorescent material selectively chosen to absorbthat energy. The emission energy from this fluorescent material will bedownshifted to a lower energy and can be absorbed by a secondfluorescent material selected for its ability to absorb such radiation.Additional fluorescent materials can be chosen that further exhibitStokes shifts until a selected emission is achieved. The selectedemission can be chosen to be partially or fully in the infrared regionsof the electromagnetic spectrum. Generally, a Stokes shift for a singlephotoluminescent phosphorescent or photoluminescent fluorescent materialranges from 20 to 100 nm. In order to produce longer Stokes shifts,multiple photoluminescent fluorescent materials can be used to produce acascading Stokes shift. A cascading Stokes shift is produced bysuccessive absorptions of the emission of one of the photoluminescentmaterials by another of the photoluminescent fluorescent materials andre-emission at a longer wavelength. When done multiple times Stokesshifts significantly in excess of 50 nm can be created.

As stated above, the photoluminescent layer may contain onlyphotoluminescent fluorescent materials. These materials can be chargedor activated by a wide range of electromagnetic radiation from UV toinfrared. The fluorescent materials are chosen, as described above, toexhibit cascading Stokes shifts to create a selected emission, which ispartially of fully in the infrared regions of the electromagneticspectrum.

It should be clearly pointed out that when the photoluminescent layercontains a selected combination of phosphorescent and fluorescentmaterials, it enables the spatial and temporal decoupling of thephotoluminescent layer and enables stealth detection. When thesemarking, whether stealth or not, are activated, emission continues longafter the activating energy has been removed or turned off, allowing fordetection to occur at a later time, and under stealth conditions.Because the emission continues after activation, the marking, or objectcontaining the marking, can be moved far away from the activating sourceand detected under stealth conditions, that is, the marking does notneed to be activated during detection and furthermore the emission fromthe marking is not detectable with the naked eye.

Suitable phosphorescent materials are the well known metal sulfidephosphors such as ZnCdS:CulAl, ZnCdS:Ag:Al, ZnS:Ag:Al, ZnS:Cu:Al asdescribed in U.S. Pat. No. 3,595,804 and metal sulfides that areco-activated with rare earth elements such as those describe in U.S.Pat. No. 3,957,678. Phosphors that are higher in luminous intensity andlonger in luminous persistence than the metal sulfide pigments that aresuitable for the present invention include compositions comprising ahost material that is generally an alkaline earth aluminate, or analkaline earth silicate. Examples of such photoluminescent phosphors areas described in U.S. Pat. No. 5,424,006.

High emission intensity and persistence phosphorescent materials can bealkaline earth aluminate oxides having the formula MO. mAl₂O₃:Eu²⁺, R³⁺wherein m is a number ranging from 1.6 to about 2.2, M is an alkalineearth metal (strontium, calcium or barium), Eu²⁺ is an activator, and Ris one or more trivalent rare earth materials of the lanthanide series,yttrium or bismuth co-activators. Examples of such phosphors aredescribed in U.S. Pat. No. 6,117,362.

High emission intensity and persistence phosphors can also be alkalineearth aluminate oxides having the formula M_(k) Al₂0₄:2XEu²⁺, 2yR³⁺wherein k−1-2x−2y, x is a number ranging from about 0.0001 to about0.05, y is a number ranging from about x to 3x, M is an alkaline earthmetal (strontium, calcium or barium), Eu²⁺ is an activator, and R is oneor more trivalent rare earth materials (e.g. lanthanum, cerium,praseodymium, neodymium, samarium, gadolinium, terbium, dysprosium,holmium, erbium, thulium, ytterbium, lutetium), yttrium or bismuthco-activators. Examples of such phosphors are described in U.S. Pat. No.6,267,911B1.

Phosphors that can be used in this invention also include those in whicha portion of the Al³⁺ in the host matrix is replaced with divalent ionssuch as Mg²⁺ or Zn²⁺ and those in which the alkaline earth metal ion(M²⁺) is replaced with a monovalent alkali metal ion such as Li^(−t),Na⁺′K⁺ Cs⁺ or Rb⁺. Examples of such phosphors are described in U.S. Pat.No. 6,117,362 & U.S. Pat. No. 6,267,911B1.

High intensity and high persistence silicates can be used in thisinvention such as has been reported in U.S. Pat. No. 5,839,718. Otherphosphorescent materials suitable for this invention can be found inU.S. Pat. No. 5,885,483. Alkaline earth aluminates of the type MAl₂0₄,which are described in U.S. Pat. No. 5,424,006, are also suitable forthis invention.

Phosphorescent materials described above generally absorb in the UV ornear UV/Visible regions of the electromagnetic spectrum.

As can be appreciated, many other phosphors are useful to the presentinvention. Such useful phosphors are described in Yen and Weber,Inorganic phosphors: compositions, preparation and optical properties,CRC Press, 2004.

Selected photoluminescent fluorescent materials useful in the currentinvention in either the photoluminescent underlayer or a functionaloverlayer include photoluminescent fluorescent materials that absorb inthe visible and/or infrared region of the electromagnetic spectrum andemit in the visible and/or infrared region. For example,photoluminescent fluorescent materials that absorb in the visible andemit in the visible region include, but are not limited to, for example,coumarins such as coumarin 4, coumarin 6, and coumarin 337; rhodaminessuch as rhodamine 6G, rhodamine B, rhodamine 101, rhodamine 19,rhodamine 110, and sulfarhodamine B; phenoxazones including Nile red andcresyl violet; styryls; carbostyryls; stilbenes; oxazines, cyanine dyes,pyrromethene, perylene dyes and fluorescenes. Examples ofphotoluminescent fluorescent materials that absorb in the visible regionof the electromagnetic spectrum and emit in the far visible and infraredregions include, but are not limited to, for example, Nile Blue, IR 140(CAS#53655-17-7), IR 125 (CAS#3599-32-4), and DTTCI (CAS#3071-70-3).Depending upon the desired infrared wavelength emitting from themarkings, fluorescent materials useful in this invention can alsoinclude, for example, materials that absorb in the infrared and emit inthe infrared. Below in Table 1 are the absorption and emissioncharacteristics of some of the photoluminescent fluorescent materialssuitable for the current invention.

TABLE 1 Max. Max. Absorbance Emission Fluorescent CAS # (nm) (nm)Coumarin 6 38215-35-0 458 505 Rhodamine 110 13558-31-1 510 535 Rhodamine19P 62669-66-3 528 565 Rhodamine 6G 989-38-8 530 556 Nile red 7385-67-3550 650 Nile blue 53340-16-2 633 672 IR 676 56289-64-6 676 720 IR-676 is1,1′,3,3,3′,3r-Hexamethy1-4,5,4′,5′-dibenzoindodicarbocyanine

The quantum efficiency of compositions comprising photoluminescentphosphorescent and/or photoluminescent fluorescent materials will bedependent on a number of factors, such as degree of overlap between theemission spectrum of one of the photoluminescent materials with theabsorption spectrum of another of the photoluminescent materials and thedegree to which the photoluminescent fluorescent materials aremolecularly dispersed that is, the aggregation state of the fluorescentmaterials in the polymer comprising the binding matrix. For thephotoluminescent fluorescent materials to be in a very fine state ofaggregation in the polymer, it is essential for the photoluminescentfluorescent materials to be in solution in the liquid carrier medium andbe compatible with the chosen polymers. It is however possible topreselect an appropriate polymer, dissolve the dye in a suitablesolvent, and upon subsequent drying end up with a fluorescent particlewhich then can be used in the photoluminescent layer.

Selected admixing of photoluminescent phosphorescent materials withphotoluminescent fluorescent materials will result in compositions thatcan be charged or activated by incident electromagnetic energy, forexample, by UV and/or short blue visible radiation, and emit partiallyor fully in the infrared. Since the activated photoluminescentphosphorescent material will continue to emit radiation long after theactivating radiation has been removed, the photoluminescent compositionwill continue to emit radiation partially or fully in the infraredregion of the electromagnetic spectrum.

As stated above, the photoluminescent layer contains one or morephotoluminescent phosphorescent materials, or one or morephotoluminescent fluorescent materials or combinations thereof. Inaddition, the photoluminescent layer, as well as the functionaloverlayers, also contains one or more liquid carriers, and one or morepolymeric binders. Optionally the layers may contain one or morephotostabilizers, one or more rheology modifiers, and one or moredispersing agents.

Beyond the selection of the photoluminescent phosphorescent materialsand/or any additional photoluminescent fluorescent materials used toenhance their performance, it should be noted that the emissionintensity and/or persistence from a photoluminescent composition isgreatly affected by both the way in which the photoluminescentphosphorescent materials are distributed and the additives used, as wellas the manner in which that composition is applied.

The improper selection and use of the composition materials, such asbinders, dispersing agents, wetting agents, rheology modifiers,photostabilizers, and the like can diminish the emission intensityemanating from the composition. This can occur, for example, due toagglomeration or settling of photoluminescent phosphorescent particles,either during handling of the formulated materials or after applicationof the formulated materials. The reduction in emission intensity and/orpersistence can result from incomplete excitations and/or scattering ofemitted radiation. The scattering of photoluminescent emissions can beeither due to agglomeration of photoluminescent phosphorescent materialor as a consequence of electromagnetic radiation scattering by one ormore of the additives selected to stabilize the photoluminescentphosphorescent pigment dispersion. The net result will be lower emissionintensity and persistence.

It is important to select only those polymeric binder resins that do notinterfere with the charging or activating radiation or with the emissionradiation and that are also compatible with the selectedphotoluminescent materials. It is also desirable that the chosenpolymeric materials should have minimal impact on the emissionintensity, that is, it should not exhibit any significant quenching ofthe photo luminance.

Binder resins suitable for the inventive compositions for thephotoluminescent layer and the functional overlayers include acrylates,for example NeoCryl® B-818, NeoCryl® B735, NeoCryl® B-813, andcombinations thereof, all of which are available from DSM NeoResins®,polyvinyl chlorides, polyurethanes, polycarbonates, polyesters, andnylons such as Nylon 6 or Nylon 6,6 and combinations thereof.

The liquid carrier for the photoluminescent layer and the functionaloverlayers can be, for example, any solvent which does not adverselyimpact the photoluminescent materials and which allows for thesolubility of the photoluminescent fluorescent materials selected forthe photoluminescent composition. Suitable liquid carriers includeglycols, glycol ethers, glycol acetates, ketones, and hydrocarbons suchas toluene and xylene.

Suitable rheology modifiers for the photoluminescent layer and thefunctional overlayers include polymeric urea urethanes and modifiedureas, for example, BYK® 410 and BYK® 411 from BYK-Chemie®.

Dispersants suitable for the inventive compositions for thephotoluminescent layer and the functional overlayers include acrylicacid-acrylamide polymers, salts of amine functional compounds and acids,hydroxyl functional carboxylic acid esters with pigment affinity groups,and combinations thereof, for example DISPERBYKO-180, DISPERBYK®-181,DISPERBYK®-108, all from BYK-Chemie® and TECO® Dispers 710 from DegussaGmbH.

Other additives for the photoluminescent layer and the functionaloverlayers can be incorporated into the inventive compositions,including wetting agents such as polyether siloxane copolymers, forexample, TEGO® Wet 270 and non-ionic organic surfactants, for exampleTEGO® Wet 500, and combinations thereof; and including deaerators anddefoamers such as organic modified polysiloxanes, for example, TEGO®Airex 900.

According to the present invention the photoluminescent layer isformulated with the following components: 10%-50% binder resin, 15%-60%liquid carrier, 15%-55% photoluminescent phosphorescent material,0.5%-10.0% dispersing agent, 0.2%-5.0% rheology modifying agent,0.1%-3.0% photostabilizer, 0.1%-2.0% de-aerating agent, 0.1%-3.0%wetting agent, and 0.0001%-0.11% photoluminescent fluorescent material.

Components of the functional overlayers designed for color alterationcan be from 10%-50% of binder resin, about 15%-50% of liquid carrier,0.5%-5.0% dispersing agent, 0.2%-3.0% rheology modifying agent,0.1%-3.0% photostabilizer, 0.2%-2.0% de-aerating agent, 0.2%-3.0%wetting agent, and 0.2%-2.0% colorant.

Components of the functional overlayers designed for photolyticstabilization or for enhancing infrared detectability in daylight can befrom 10%-75% of binder resin, about 15%-50% of liquid carrier, 0.5%-5.0%dispersing agent, 0.2%-3.0% rheology modifying agent, 0.1%-3.0%photostabilizer, 0.2%-2.0% de-aerating agent, 0.2%-3.0% wetting agent,and 0.0005%-2.0% photoluminescent fluorescent material.

The functional overlayer that is formulated to alter the daytime colorso as to be a stealth marking contains colorants chosen to match thedaylight color of the object to which the stealth marking is applied,and hence blends in. In other applications, wherein the stealth markingis applied to objects that typically have non-stealth markings fortraditional usage, such as, for example, a roadway marking or anidentifying logo etc, the functional overlayer contains colorants thatwould render a daylight color indicative to a casual observer of thepresence of such traditional markings and not a marking deployed forstealth detection. The colorants are further chosen for their ability toallow charging radiation to pass through the functional overlayer aswell as the resultant infrared radiation to pass through. Suitablecolorants can be chosen by performing spectroanalysis, particularlyabsorbance/fluorescence scans in the UV, visible and infrared regions ofthe spectrum. Thus, useful colorants will be those that exhibit lowabsorbance in both the excitation spectrum of the phosphorescentmaterials in the photoluminescent layer as well as in the final emissiveregion. Using this technique, a broad spectrum of colorants, such asfrom violet to yellow to brown to red, can be found that can beformulated into the functional overlayer. To obtain a specific daytimecolor, the functional overlayer may be formulated with more than onecolorant. Examples of colorants that meet the aforementioned criteriaare described in the set of examples below.

The functional overlayer that is formulated to improve photolyticstability contains materials chosen with absorptions in specific regionswhich are detrimental to the photolytic stability of thephotoluminescent materials in the underlying photoluminescent layer. Thefirst step is to determine the damaging radiation for one or more of thephotoluminescent materials in the photoluminescent layer. The next stepis to choose colorants that not only absorb the damaging radiation butalso have the least interference in the excitation spectrum of thephotoluminescent materials such as the excitation spectrum of thephosphorescent materials and the final emissive region. Suitablecolorants can be chosen by performing spectroanalysis, particularlyabsorbance/fluorescence scans in the UV, visible and infrared regions ofthe spectrum.

The functional overlayer that is formulated to improve daylightdetectability of the infrared emissions from the markings containsfluorescent materials that are chosen to convert radiation incident uponthe marking in daylight either indoors or outdoors, includingenvironments with artificial light sources. The fluorescent materialsare selected such that the emission of one materials overlaps with theabsorbance of another fluorescent material with this being repeated(similar to selection processes in the photoluminescent underlayer) toeffectively cascade the incident radiation into the infrared region ofthe spectrum. Fluorescent materials in the functional overlayer can beselected to convert specific radiation (including that from artificialsources) into infrared radiation.

A functional overlayer can also be formulated to camouflage a hiddenmessage that will not be observable with the naked eye but with the useof appropriate equipment can be observed. If the message is printed withmaterials that absorb visible radiation then the functional overlayerwill contain materials that absorb that same particular visibleradiation so as to render it invisible.

Beyond the selection of the colorants, the functional overlayer willinclude, for example, one or more liquid carriers, and one or morepolymeric binders. Optionally the functional overlayer may contain oneor more photostabilizers, one or more rheology modifiers, and one ormore dispersing agents. The specifics of these materials have beenmentioned above in association with the photoluminescent layers.

Photostabilizers useful in the inventive composition include UVabsorbers, singlet oxygen scavengers, antioxidants, and/or mixturesthereof, for example, Tinuvin® 292, Tinuvin® 405, Chimassorb® 20202,Tinuvin® 328, or combinations thereof, all from Ciba® SpecialtyChemicals.

The present invention also provides for a reflective layer to be presentunder the photoluminescent layer that is designed to reflect UV, visibleand infrared radiation out through the stealth marking. This will helpto intensify the selected infrared emission. The reflecting layer may beany layer that reflects the selected light and includes, for example,formulations that include materials, such as white pigments, such as,for example, titanium oxide that will reflect the photoluminescenceemitted from the photoluminescent layer. The reflective layer may be apreformed metal layer, such as, for example, aluminum that will reflectthe photoluminescence.

The present invention also relates to methods of creating and usingphosphorescent stealth markings.

Photoluminescent objects of the current invention may be made by any ofthe known methods of manufacture including extrusion or molding toprovide solid objects, or coating on surfaces of objects, using a numberof coating techniques including spray, dip, lamination, electrostatic,screen, roller, curtain, slot coating or other methods well known in theart.

In coating applications, the photoluminescent layer is coated and driedto provide a photoluminescent layer which emits fully or partially inthe infrared region of the electromagnetic spectrum. The functionaloverlayer is then applied using the same or different coating techniqueas the photoluminescent layer and then dried. This process is continueduntil all desired functional coatings have been applied.

The photoluminescent underlayer may only cover a portion of the object.For example, in cases where messages, indicia, graphics or other designfunctionality is designed the photoluminescent layer may be printed ontothe object using such techniques as offset, gravure, letterpress, screenor other printing technique. It should be noted that the functionaloverlayer is applied to ensure the photoluminescent underlayer iscovered.

It should be noted that the functional overlayer may also act as a topcoat that protects the marking from various unfriendly environmentaland/or handling conditions.

An alternative method of manufacture is to first apply the functionaloverlayer to a supporting film, such as, for example, Mylar®, followedby drying. Additional functional overcoats are then applied and dried.The coated support film is then placed over a previously coated anddried photoluminescent layer with the functional overlayer in contactwith the photoluminescent layer. Pressure is then applied, andoptionally heat, to provide intimate contact between the film containingthe functional overlayer, or overlayers, and the photoluminescent layer.The support film may then be removed to create a photoluminescentstealth marking.

The above described photoluminescent markings can be used for thepurposes of stealth marking, as previously described. The objectscontaining stealth markings can be charged or activated withelectromagnetic radiation, for example, ultraviolet, near ultraviolet orcombinations thereof, by a number of convenient methods including metalhalide lamps, fluorescent lamps, or any light source containing asufficient amount of the appropriate visible radiation, UV radiation orboth, as well as sunlight, either directly or diffusely, including suchtimes when sunlight is seemingly blocked by clouds. At those timessufficient radiation is present to charge or activate the markingsand/or objects containing the markings.

It can readily be seen that activation of the inventive markings anddetection of their subsequent emission, can occur at separate times andat separate places. The source of activation can be removed and themarkings and/or objects containing the markings will continue to emitradiation in the selected region and be detected, for example, indarkness when there is no activating radiation. Since no activation isrequired at the time of detection, the possibility of revealing theposition of a stealth operator is eliminated. When used for stealthpurposes the stealth markings and objects containing the marking canalso be detected at long distances from the stealth operator so that theoperator's position may be hidden, further adding to the stealth abilityof the current invention. For the purpose of identification orauthentication, stealth or otherwise, a detector that will detect theselected emission signature from the photoluminescent stealth markingsand/or objects containing the markings is used. An example of adetection apparatus with amplification is night vision apparatus. Nightvision apparatus can detect either visible radiation if present,infrared radiation, or both visible and infrared radiation. Thedetection apparatus can be designed to detect specific emissionsignatures. Where necessary, detectors can incorporate amplificationcapabilities. The detector can be designed to read a specific wavelengthof the emission signature of the stealth markings and/or objectscontaining the marking as well as the photoluminescent stealth markingcan be created to emit radiation suitable for a specific detector. Asmentioned, because of the nature of the inventive stealth methods andstealth markings, when the markings are enabled for stealth detection,detection can occur at a time and place separate from activation.

Under certain conditions the detection equipment may be adverselyimpacted by radiation from extraneous sources causing identification ordetection of the intended markings and/or objects containing themarkings to be difficult due to the inability of the detector todifferentiate between emission signature and such spurious radiation.Under these conditions, the detection equipment, for example, nightvision apparatus may be fitted with a filter designed to eliminate theextraneous visible radiation, thereby enhancing identification ordetection.

The type of image obtained from the selected emission signature can bein the form of a general image emitted by the stealth markings and/orobjects containing the marking or it may be in the form of a pattern. Itcan also have informational properties in the form of alphabetical,numerical, or alpha-numeric markings as well as patterns and symbols,such as geometric shapes and designations. In this manner, the stealthdetection and identification can be topical, either with up-to-dateinformation, such as times and dates, as well as for messages.

When practicing stealth identification, for the case wherein theemission is only partially in the infrared region of the electromagneticspectrum, to enhance the undetectability of the visible emission, thefunctional overlayer is adjusted to absorb such visible radiationthereby further ensuring undetectability by a human observer. Stealthdetection and identification described above, either for stealthmarkings or objects containing such stealth markings, can only be madeby using devices designed to detect the selected emission signature.

Detection and identification methods using the current photoluminescentmarkings and/or objects containing the markings can be deployed fordetection and identification of objects, people or animals.Photoluminescent markings can be applied to, for example, militaryobjects to designate friend or foe, as well as trail markings. When suchmarkings are rendered as stealth markings and enabled for stealthdetection such stealth markings can be designed to be detected only byselected personnel. Examples of the use of stealth markings for stealthdetection include airplane or helicopter landing areas, or stealthmarkings that reveal the presence or absence of friendly forces.

Detection and identification methods using the current photoluminescentmarkings and/or objects containing the marking allow for stealthidentification, or otherwise, of, for example, stationary combatapparatus, mobile combat apparatus, combat articles of clothing orcombat gear either worn by combatants or carried by combatants, tanks,stationary artillery, mobile artillery, personnel carriers, helicopters,airplanes, ships, submarines, rifles, rocket launchers, semi-automaticweapons, automatic weapons, mines, diving equipment, diving clothing,knap-sacks, helmets, protective gear, parachutes, and water bottles.

The current photoluminescent markings and/or objects containing themarking allow for stealth detection and identification, or otherwise,including tagging, tracking and locating transportation vehicles, suchas, for example, buses, airplanes, taxi cabs, subway vehicles,automobiles and motorcycles.

Detection and identification methods using the current photoluminescentstealth markings and/or object containing the marking, whether enabledfor stealth detection or not, can also be used for applications such asin sports and entertainment such as, for example, in hunting and fishingapplications which are designed to identify or detect other hunters orfisherman. Stealth markings can be particularly useful in huntingapplications such as, for example, vests, pants, shirts or jackets andthe like, wherein accidents can be avoided by using infrared emissiondetection apparatus for stealthily identifying or detecting otherhunters but at the same time, since no visible emission is detectable,avoiding spooking the hunted animal.

Stealth detection and identification compositions that embody stealthmarkings may be particularly useful for applications requiring security.

The stealth markings and/or object containing the marking of the currentphotoluminescent stealth markings can also be used in anti-counterfeitapplications applicable to a wide variety of goods or objects.Photoluminescent stealth markings and/or objects containing the markingsprepared according to the methods described above can be utilized inanti-counterfeit applications such as, for example, currency,anti-piracy applications, such as CDs or DVDs, luxury goods, sportinggoods etc. In many of these applications it becomes important that thepotential counterfeiter be unaware that the object that is beingcounterfeited contains a marking and/or object containing the markingthat will authenticate the object. The stealth marking can also be codedsuch as a date code or other identifying code that a counterfeitedobject would not have.

The current photoluminescent markings can be applied onto carriermaterials, such as films, for example, polyester, polycarbonate,polyethylene, polypropylene, polystyrene, rubber or polyvinyl chloridefilms, or metallic plates, for example, aluminum, copper, zinc, brass,silver, gold, tin, or bronze plates. Other layers can be added to thecarrier material such as an adherent material, for example, an adhesivewith high or low peel strength or a magnetic material. The carriermaterial with the photoluminescent markings and/or objects containingthe marking applied thereon can either be attached permanently to anobject or it can be transferable so that detection and identificationcan be changed, updated or removed. Such application allows for anobject to have the detection and identification capabilities of thecurrent invention without the object itself undergoing a fabricationprocess. In this application, if information becomes outdated, thecarrier material with the photoluminescent stealth markings in the formof a removable film or plate can be replaced by another carrier materialwith the photoluminescent stealth marking with updated information suchas, for example, in safety applications or security applications.

Objects prepared using the current photoluminescent markings and/orobjects containing the marking can have low emission intensity by virtueof inadequate reflection of the emitted electromagnetic radiation,either because of surface roughness or because of materials in theobject that are absorptive of the selected emission signature. As aresult reflective layers or coatings that are reflective of theemissions from the photoluminescent compositions can be used as primersto provide a surface from which the emission signature can reflect.Hence a reflective layer may be first applied either onto a carriermaterial or onto the object itself followed by one or morephotoluminescent markings of the current invention.

In applications including camouflage patterns, or other patterns, morethan one color may be used in the functional overlayer. For example,some camouflage, such as desert camouflage, contains four colorcombinations: tan, brown, dark brown and black. Therefore applyingphotoluminescent stealth markings to desert camouflage require applyinga photoluminescent layer followed by application of a functionaloverlayer which contains tan, brown, dark brown and black arranged tomimic the desert camouflage pattern. In this way the photoluminescentemission blends in with the camouflage background.

EXAMPLES Example 1 Stealth Marking

Infrared Emitting Photoluminescent Layer:

Into 54.47 g of ethylene glycol monobutyl ether was admixed 20.35 g ofNeoCryl® B-818 (an acrylic resin from DSMNeoResins®). To the admix wasadded 1.80 g of DisperBYK® 180 (from BYK-Chemie), 0.88 g of TEGO® Wet270 and 0.57 g of TEGO® Airex 900 (both from Degussa GmbH) withstirring. Then 0.10 g of rhodamine 19P, 0.10 g of dichlorofluorescein,0.10 g of Nile Blue, 0.10 g of Nile Red, 0.05 g of sulfarhodamine B,0.01 g of rhodamine 800 and 0.01 g of 3,3′-diethyloxatricarbocyanineiodide were added and mixed until dissolved. 20.35 g of H-13, greenphosphor (from Capricorn Specialty Chemicals) was then added. 1.11 g ofBYK® 410 (from BYK-Chemie), was then added. The photoluminescentcomposition thus prepared was coated onto a violet colored wall panelusing a wire draw down bar, and dried at 50° C. (<5% solvent) for 12hours to a dried thickness of 10 mils.

Functional Overlayer #1:

To 91.34 g of Hauthane L-3058 (from C. L. Hauthaway Corp.) was admixed1.82 g of TEGO® Wet 270 and 1.82 g of Tinuvin® 1130 (from Ciba SpecialtyChemicals). To this admixture was added 0.45 g of ORCOBRITE™ PigmentViolet 4BN (from Organic Dyestuffs Corp) and mixing was continued for 30min. Additional Pigment Violet 4BN was added until the functional layermatched the violet color of the wall panel when coated and dried. Mixingwas stopped and the composition was allowed to stand for 1 hr. Thecomposition was coated over the photoluminescent layer using a wire drawdown bar and dried at 35′C for 2 hours to a dried thickness of 3 mils.When dried, the coatings could not be distinguished from the violetcolored wall panel and no luminescence was observed.

The wall panel was illuminated by a 150 watt metal halide lamp placed 1foot away for 15 minutes. The lamp was removed and the room in which thewall panel resided was made pitch black. Over the course of adjusting tothe dark, no luminescence could be observed. One hour after removal ofthe lamp, a Generation 3 proprietary night vision monocular scope wasused to observe the wall from a distance of 10 feet. A bright image ofthe photoluminescent layer was readily seen.

Functional Overlayer #2:

The process of Example 1 was repeated with the following exceptions:

1) The wall panel that was coated was blue violet

2) 0.15 g of ORCOBRITE™ Pigment Blue 3GN 2031 (from Organic DyestuffsCorp) was added to the functional overlayer composition in place of thePigment Violet 4BN, with additional dye added if necessary, whichresulted in a blue violet overlayer which matched the color of thecoated wall panel when dried as described.

Again no luminescence was observed either in ambient light or underpitch black conditions while a bright image was observed when aGeneration 3 proprietary night vision monocular scope.

Thus it can be seen that a photoluminescent infrared emitting layer canbe overcoated with a functional overlayer that is formulated to coverthe emitting layer and hide it from unaided viewing by blending with thebackground while at the same time allowing both activating radiation andinfrared emission to pass through. For different colored backgrounds thefunctional overlayer can be formulated to color-match the background.For situations, such as road markings or doorframes, where a marking isalready present the functional overlayer can be formulated to simulatesuch a marking.

Example 2 Marking with Overlayer to Provide Photolytic Stability

Infrared Emitting Photoluminescent Composition

Into 54.47 g of ethylene glycol monobutyl ether was admixed 20.35 g ofNeoCryl® B-818 (an acrylic resin from DSM NeoResins®). To the admix wasadded 1.80 g of DisperBYK® 180 (from BYK-Chemie), 0.88 g of TEGO® Wet270 and 0.57 g of TEGO® Airex 900 (both from Degussa GmbH) withstirring. Then 0.10 g of rhodamine 19P, 0.10 g of dichlorofluorescein,0.10 g of Nile Blue, 0.10 g of Nile Red, 0.05 g of sulfarhodamine B,0.01 g of rhodamine 800 and 0.01 g of 3,3′-diethyloxatricarbocyanineiodide were added and mixed until dissolved. 20.35 g of H-13, greenphosphor (from Capricorn Specialty Chemicals) was then added withmixing. 1.11 g of BYK® 410 (from BYK-Chemie) was then added with mixing.

Functional Overlayer Composition #3:

To 91.34 g of Hauthane L-3058 (from C. L. Hauthaway Corp.) were admixed1.82 g of TEGO® Wet 270 and 1.82 g of Tinuvin® 1130 (from Ciba SpecialtyChemicals). To this admixture was added 0.30 g of ORCOBRITE™ PigmentViolet 4BN, 0.08 g of ORCOBRITE™ Pigment Blue 3G and 0.15 g ofORCOBRITE™ Pigment yellow 4GX HLF (all from Organic Dyestuffs Corp) andmixing was continued for 30 min. Mixing was stopped and the compositionwas allowed to stand for 1 hr.

Functional Overlayer Composition #4:

To 91.34 g of Hauthane L-3058 (from C. L. Hauthaway Corp.) was admixed1.82 g of TEGO® Wet 270 and 1.82 g of Tinuvin® 1130 (from Ciba SpecialtyChemicals). To this admixture was added 0.30 g of ORCOBRITE™ PigmentViolet 4BN, 0.08 g of ORCOBRITE™ Pigment Blue 3G and 0.30 g ofORCOBRITE™ Pigment yellow 4GX ELF (all from Organic Dyestuffs Corp) andmixing was continued for 30 min. Mixing was stopped and the compositionwas allowed to stand for 1 hr.

Infrared Emitting Photoluminescent Markings

A) The photoluminescent composition was coated onto 10 mil whitepolyethylene terephthalate using a wire draw down bar, and dried at 50°C. (<5% solvent) for 12 hours to a dried thickness of 6.80 mils.

B) The photoluminescent marking from A) was overcoated with functionalcomposition #3 using a Bird-style applicator and dried 35° C. (<5%solvent) for 2 hours to a dried thickness of 1.75 mils.

C) The photoluminescent marking from A) was overcoated with functionalcomposition #4 using a Bird-style applicator and dried 35° C. (<5%solvent) for 2 hours to a dried thickness of 1.75 mils.

Photolytic Stability Study

The IR emitting photoluminescent markings, A-C above, were charged in alight chamber consisting of blue actinic and cool white fluorescentlamps with an energy output of 1410 foot-candles as measured by anExtech LT 300 Light Meter. The markings were placed at a distance of 3inches from the lights for 10 minutes. The now charged material wasplaced in a light tight chamber and the emitting energy was measuredusing an International Light High-Gain Detector, Model #SHD033/11,equipped with a silicon photodiode detector. Measurements was made usinga high-pass SCS695 filter #27398 which measured all emission above 695nm, before and after exposure to photolysis.

The IR emitting photoluminescent markings, A-C above, were then testedfor output luminance after photolysing radiation. The markings wereplaced in an Atlas Ci35A Weather-o-meter using borosilicate inner andouter filters for 100 hrs. Illumination was provided by a Xenon Arc lampwith irradiance equal to 0.75 Watts/meter² at a peak output 320 nm. Thetemperature of the Weather-o-meter was 73° C. The exposed markings wereplaced in a light tight chamber and the emitting energy was measuredusing an International Light High-Gain Detector, Model #SHD033/U,equipped with a silicon photodiode detector. The measurement was madeusing a high-pass SCS695 filter #27398 from which measured all emissionabove 695 nm. The results of this study are presented in Table I.

TABLE I IR Emission IR Emission after 0 hrs after 100 hr photolysisphotolysis (mcd/m²/mil) (mcd/m²/mil) % loss A) IR EmittingPhotoluminescent 8.8 2.4 72.7% Marking B) IR Emitting Photoluminescent6.0 4.9 18.3% Marking with Functional Overlayer #3 C) IR EmittingPhotoluminescent 6.2 4.4 29.0% Marking with Functional Overlayer #4

As can readily be seen, the photolytic stability of the IR emittingphotoluminescent layer is greatly improved using either of the inventiveanti-photolysis functional compositions as an overlayer. The functionalovercoat compositions were not optimized to fully eliminate any blockingof the infrared emission. The yellow pigment used in the functionalcomposition has a characteristic absorbance that “tails” into theexcitation region of the phosphorescent material resulting in somereduction of the IR emission. Judicious selection of yellow pigments inthe formulation whose absorbencies either do not “tail” into, or arelowest in, the excitation region of the phosphorescent material, wouldhave resulted in a higher retention of infrared emission.

1. A photoluminescent marking comprising: a photoluminescent layercomprising at least one type of photoluminescent material; and at leastone functional overlayer disposed over at least the photoluminescentlayer, the at least one functional overlayer being adapted toselectively filter wavelengths of radiation to enhance the daylightobservability of a final emission signature of the marking.
 2. Themarking as in claim 1, wherein the at least one functional overlayercomprises at least one selectively reflective material adapted toreflect selected emissions from the at least one type ofphotoluminescent material back into the photoluminescent layer.
 3. Themarking as in claim 1, wherein the at least one functional overlayercomprises at least one selectively reflective material that issubstantially transmissive of selected wavelengths.
 4. The marking as inclaim 1, wherein the selected wavelengths comprise at least one ofinfrared wavelengths, visible wavelengths, and ultraviolet wavelengthsof electromagnetic radiation.
 5. The marking as in claim 1, wherein theat least one type of photoluminescent material is at least onephosphorescent material, at least one fluorescent material, or anycombination thereof.
 6. The marking as in claim 1, wherein the at leastone functional overlayer comprises at least one colorant.
 7. The markingas in claim 1, wherein the at least one type of photoluminescentmaterial comprises at least one high persistence phosphor.
 8. Themarking as in claim 1, wherein the final emission signature of themarking emits in at least one of an infrared, a visible, and anultraviolet domain of the electromagnetic spectrum.
 9. The marking as inclaim 1, further comprising a reflective layer, said reflective layerredirects electromagnetic radiation to the viewing hemisphere.
 10. Aphotoluminescent marking comprising: a photoluminescent layer comprisingat least one type of photoluminescent material; and at least onefunctional overlayer disposed over at least the photoluminescent layer,the at least one functional overlayer being adapted to selectivelyfilter wavelengths of radiation to prevent the observability with thenaked eye of a printed message on the marking.
 11. The marking as inclaim 10, wherein the at least one functional overlayer comprises atleast one colorant that absorbs selective wavelengths of radiationdisposed over the printed message.
 12. The marking as in claim 11,wherein the at least one colorant comprises at least one absorptivematerial.
 13. The marking as in claim 11, wherein the at least onefunctional overlayer further comprises at least one selectivelyreflective material that is substantially transmissive of selectedwavelengths.
 14. The marking as in claim 10, wherein the at least onefunctional overlayer comprises at least one selectively reflectivematerial adapted to reflect selected emissions from the at least onetype of photoluminescent material back into the photoluminescent layer.15. The marking as in claim 10, wherein the at least one functionaloverlayer comprises at least one selectively reflective material that issubstantially transmissive of selected wavelengths.
 16. The marking asin claim 10, wherein the at least one type of photoluminescent materialis at least one phosphorescent material, at least one fluorescentmaterial, or any combination thereof.
 17. The marking as in claim 10,wherein the at least one type of photoluminescent material comprises atleast one high persistence phosphor.
 18. The marking as in claim 10,wherein the marking emits an emission signature that is in at least oneof an infrared, a visible, and an ultraviolet domain of theelectromagnetic spectrum.
 19. The marking as in claim 10, furthercomprising a reflective layer, said reflective layer redirectselectromagnetic radiation to the viewing hemisphere.
 20. A method offabricating a marking, the method comprising: forming a photoluminescentlayer comprising at least one type of photoluminescent material;applying at least one functional overlayer to the photoluminescentlayer, the at least one functional overlayer being adapted toselectively filter wavelengths of radiation; and incorporating thephotoluminescent layer and the at least one functional overlayer onto orinto at least a portion of the marking.
 21. The method as in claim 20,further comprising adapting the marking for association with an object.22. The method as in claim 20, wherein the marking emits an emissionsignature that is in at least one of an infrared, a visible, and anultraviolet domain of the electromagnetic spectrum.
 23. The method as inclaim 20, wherein forming comprises mixing the at least one type ofphotoluminescent material into a combination of at least one binderresin and at least one liquid carrier.
 24. The method as in claim 20,wherein the at least one functional overlayer comprises at least onecolorant.
 25. The method as in claim 24, wherein the at least onecolorant comprises at least one absorptive material.
 26. The method asin claim 20, wherein the at least one functional overlayer comprises atleast one selectively reflective material adapted to reflect selectedemissions from the at least one type of photoluminescent material backinto the photoluminescent layer.
 27. The method as in claim 20, whereinthe at least one functional overlayer comprises at least one selectivelyreflective material that is substantially transmissive of selectedwavelengths.
 28. The method as in claim 20, wherein the at least onetype of photoluminescent material is at least one phosphorescentmaterial, at least one fluorescent material, or any combination thereof.29. The method as in claim 20, wherein the at least one type ofphotoluminescent material comprises at least one high persistencephosphor.
 30. The method as in claim 20, further comprisingincorporating at least one reflective layer onto or into at least aportion of the marking.
 31. A method for marking an object, the methodcomprising: applying a photoluminescent marking onto or into at least aportion of the object, the photoluminescent marking comprising aphotoluminescent layer and at least one functional overlayer that isadapted to selectively filter wavelengths of radiation.
 32. The methodas in claim 31, wherein applying comprises at least one of incorporatingthe photoluminescent marking into the object during manufacture,building the photoluminescent marking on the object, and later affixingthe photoluminescent marking to the object.
 33. The method as in claim31, wherein the photoluminescent marking further comprises at least onereflective layer.
 34. A method for identifying an object, the methodcomprising: detecting a potential emission signature from aphotoluminescent marking previously applied onto or into at least aportion of the object, the photoluminescent marking comprising: aphotoluminescent layer, and at least one functional overlayer that isadapted to selectively filter wavelengths of radiation, and wherein thepotential emission signature is subsequently compared to a knownemission signature.
 35. The method as in claim 34, wherein thephotoluminescent marking is charged or activated on the object with atleast one wavelength that is in at least one of an infrared, a visible,and an ultraviolet domain of the electromagnetic spectrum.
 36. Themethod as in claim 34, wherein the photoluminescent marking is chargedor activated on the object with at least one wavelength from at leastone of a natural source and an artificial source.
 37. The method as inclaim 34, wherein detecting comprises observing the potential emissionsignature with a detection apparatus.
 38. The method as in claim 34,wherein the photoluminescent marking further comprises at least onereflective layer.
 39. The method as in claim 34, wherein the potentialemission signature is in at least one of an infrared, a visible, and anultraviolet domain of the electromagnetic spectrum.